Compressor and turbine rotors are formed of one or more disks, each carrying a plurality of blades. The disk structure must resist bending caused by the blades and vibration of the blades. Of particular importance in high speed applications is the strength of the disk structure which must resist the centrifugal forces of the blades, the blade attachments, and the disk itself. Only structure providing full hoop path is live load which resists the centrifugal force. Lapped construction where one of the members is not a full hoop creates dead load which increases a load but does not contribute to the strength. The thickness of the disk material remote from the rotational center line is detrimental since it has higher force per unit mass and also has a higher mass because of its greater diameter.
The disk is usually wide at its outer rim to match the blade width and to appropriately resist bending forces transmitted by the blade. Conventional drum rotors have single neck blade attachments. These must be thickened beyond stress limited thickness to withstand blade vibrations.
The use of bonded attachments allows for multi-rings which can withstand vibrations at or near stress limited thicknesses. Since blades of compressors or gas turbines will experience higher temperature than the disk, it is helpful to use a construction which permits different materials for disk and blades, including blade platforms. It is also helpful to have a structure which is easily machined, not only reducing the cost but improving the quality of the product.